Temporal dynamics of the human response to symmetry

Abstract

Symmetry is a highly salient feature of animals, plants, and the constructed environment. Although the perceptual phenomenology of symmetry processing is well understood, little is known about the underlying neural mechanisms. Here we use visual evoked potentials to measure the time course of neural events associated with the extraction of symmetry in random dot fields. We presented sparse random dot patterns that were symmetric about both the vertical and horizontal axes. Symmetric patterns were alternated with random patterns of the same density every 500 msec, using new exemplars of symmetric and random patterns on each image update. Random/random exchanges were used as a control. The response to updates of random patterns was multiphasic, consisting of P65, N90, P110, N140 and P220 peaks. The response to symmetric/random sequences was indistinguishable from that for random/random sequences up to about 220 msec, after which the response to symmetric patterns became relatively more negative. Symmetry in random dot patterns thus appears to be extracted after an initial response phase that is indifferent to configuration. These results are consistent with the hypothesis (Lee, Mumford, Romero, & Lamme, 1998; Tyler & Baseler, 1998) that the symmetry property is extracted by processing in extrastriate cortex.

The Posterior Sustained Negativity Revisited—An SPN Reanalysis of Jacobsen and Höfel (2003)

“…Bertamini, Makin, and colleagues posit that the SPN is a fairly obligatory electrophysiological response that reflects the processing of symmetric stimuli, and other research has demonstrated that symmetry is an important feature extracted already early in the visual processing stream [16][17][18][19]. In the research by Jacobsen and Höfel, the posterior sustained negativity appeared to be task-dependent and/or driven by spontaneous processes.…”

Emergence of symmetry selectivity in the visual areas of the human brain: fMRI responses to symmetry presented in both frontoparallel and slanted planes

“…Together these results suggest that when attention is directed toward symmetry, responses increase, but when attention is directed away from symmetry, such as during a color task, responses decrease. This task dependence has not emerged strongly from the EEG literature on symmetry (Höfel and Jacobsen, 2007a, 2007b; Jacobsen, & Höfel, 2003; Makin, Rampone, Pecchinenda, & Bertamini, 2013; Makin et al, 2014; Norcia et al, 2002; Rampone, Makin, & Bertamini, 2014; Wright, Makin, & Bertamini, 2017); however, perhaps because of an increased sensitivity of fMRI to attentional effects, we were able to detect such differences here.…”

“…It is possible then, that the additional attentional requirements of these trial‐by‐trial color judgements led to a greater suppression of symmetry‐specific responses to slanted stimuli in the study by Makin et al (2015). It is also of note that the measured EEG symmetry response is not always task dependent and can be similar across tasks, whether people are attending to regularity or some other feature such as the color of the dots (Höfel and Jacobsen, 2007a, 2007b; Jacobsen et al, 2003; Makin et al, 2014, 2013; Norcia et al, 2002; Rampone et al, 2014; Wright et al, 2017). Such task‐dependent differences may therefore only emerge for slanted stimuli.…”

Traditional and New Principles of Perceptual Grouping

“…Such symmetrical patterns have been found to be particularly visually salient. For instance, symmetry has clear effects on detection of patterns in random dot fields, contours, and other stimuli (e.g., Machilsen, Pauwels, & Wagemans, 2009;Norcia, Candy, Pettet, Vildavski, & Tyler, 2002;. However, when a symmetrical pattern is tilted relative to the frontal plane, its features in the image projected to the retinae are no longer symmetrical.…”